A hot melt adhesive can be melted and the melted adhesive can be applied in a thin layer. Such an adhesive can exhibit a limited pot life. For example, the thin layer of adhesive can cool down very fast and solidify in such a manner that the top surface of the part to be joined is no longer tacky and no longer creates an adhesive bond. This can be the case when dealing with hot melt adhesives that are based upon amorphous thermoplastics. In addition, the adhesive can remain thermoplastic after application. This can lead to renewed melting of the adhesive in the adhesive bond upon heating of the adhesive bond which can lead to a corruption of the bond under load.
Polyurethane hot melt adhesives are reactive hot melt adhesives. They can react with moisture and cure following the application. Bonds that are thermally stable can be achieved. These adhesives can be weak immediately after their application. Such adhesives can build up their strength over time, for example, when they cure. For example, reactive polyurethane hot melt adhesives can feature a longer pot life in thin layers but can have a limited initial strength.
Hot melt adhesives which are based upon silane grafted poly-α-olefins are disclosed in, for example, U.S. Pat. No. 5,994,474 and DE 40 00 695 A1. These adhesives are hot melt adhesives and reactive hot melt adhesives, which can allow the achievement of high strength and thermal stability. At the same time, the initial strength can be very high. In thin coats these adhesives can feature a very short pot life, which can be detrimental to its use as a laminating adhesive without a prior reactivation (re-melting).
These adhesives can exhibit good adhesion to non-polar surfaces such as polypropylene or polyethylene. However the adhesion to polar substrates can be very limited.
EP 2 113 545 A1 describes a reactive hot melt adhesive which can demonstrate a long pot life and a good adhesion to non-polar substrates but limited adhesion to polar substrates.